Although bacteria and archaea are able to grow and adapted to the petrol reservoirs during severalyears, there are no results from microbial diversity of oilfields with high temperature in Iran. Hence, the present study tried to identify microbial community in non-water flooding Zeilaei (ZZ) oil reservoir.

In this study, for the first time, non-water flooded high temperature Zeilaei oilfield was analyzed for its microbial community based on next generation sequencing of 16S rRNA genes.

The results obtained from this study indicated that the most abundant bacterial community belonged to phylum of Firmicutes (Bacilli) and Thermotoga, whileother phyla (Proteobacteria, Actinobacteria and Synergistetes) were much less abundant. Bacillus subtilis, B. licheniformis, Petrotoga mobilis, P. miotherma, Fervidobacterium pennivorans, and Thermotoga subterranea were observed with high frequency. In addition, the most abundant archaea were Methanothermobacter thermautotrophicus. Discussion and

Although there are many reports on the microbial community of oil filed reservoirs, this is the first report of large quantities of Bacillus spp. from a high temperature oil reservoir.